Compression Member (Strut/Column)

A compression member (column, strut, truss top chord, bracing) carries axial compressive force, and unlike a tension member its strength is usually governed by buckling instability rather than material yielding. The key parameter is slenderness — the effective length divided by the radius of gyration (KL/r) — with the effective length factor K depending on end restraint (the classic Euler cases). Slender members fail elastically at the Euler load well below the squash load; stocky members approach yield.

IS 800 Cl. 7 uses the multiple-column-curve approach: the design compressive stress is obtained from a buckling-class curve (selected by section type and buckling axis) as a function of the non-dimensional slenderness, accounting for residual stresses and initial imperfections. Design is dominated by minimising effective length and choosing sections with a large, well-distributed radius of gyration (tubes/box vs. open sections); members must also be checked for local buckling of slender plate elements and, for beam-columns, combined axial-plus-bending interaction.